fix: rsa_crypt() resource leaks on error paths (OpenSSL 3.x)

[Koan-Bot]

Summary

• rsa_crypt() used CHECK_OPEN_SSL() (which croaks immediately) for error checking, leaking allocated resources when any OpenSSL call fails
• Replaced with THROW()/goto err pattern for proper cleanup of EVP_PKEY_CTX, OSSL_LIB_CTX, and the output buffer
• Also freed the output buffer before croaking on the PSS padding validation check

Leaked resources on error (before fix)

Failure point	to buffer	ossllibctx	ctx
PSS padding check	leaked	-	-
CTX allocation	leaked	leaked	-
init_crypt	leaked	leaked	leaked
set_padding	leaked	leaked	leaked
p_crypt (size query)	leaked	leaked	leaked
p_crypt (actual)	leaked	leaked	leaked

Test plan

• All 278 existing tests pass
• encrypt/decrypt tested in rsa.t with multiple padding modes

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🤖 Generated with Claude Code

[timlegge]

looks good